Various technologies exist for recovering hydrocarbon fluids from subterranean formations. With many of these technologies, hydrocarbon fluids are collected in a production wellbore which is positioned in a hydrocarbon containing formation. The flow of hydrocarbon fluids to the production wellbore may be driven by a variety of forces, including natural formation pressure, external pressurization of the formation, fluid injection fluid drive), a combustion front (i.e., in situ combustion) etc.
The flow of hydrocarbon fluids to the production wellbore is dependent upon the magnitude of the driving forces in the formation and upon the mobility of the hydrocarbon fluids in the formation. The mobility of hydrocarbon fluids in a subterranean formation is the ratio of the permeability of the formation to the viscosity of the hydrocarbon fluids. Mobility is therefore a function of both the properties of the hydrocarbon fluids and the properties of the subterranean formation.
For a given magnitude of driving force, the flow of hydrocarbon fluids to the production wellbore may generally be expected to increase as the mobility of the hydrocarbon fluids in the formation increases, either by decreasing the viscosity of the hydrocarbon fluids or by increasing the permeability of the formation.
Options for decreasing the viscosity of hydrocarbon fluids in a subterranean formation include increasing the temperature of the hydrocarbon fluids in the formation and diluting the hydrocarbon fluids in the formation with a less viscous fluid.
Increasing the temperature of the hydrocarbon fluids in the formation may be achieved by injecting steam into the formation in a steam assisted gravity drainage (SAGD) process, by introducing a heat source such as an electrical heater or a radio frequency heater into the formation, by in-situ combustion of the formation, or in some other manner. Diluting the hydrocarbon fluids in the formation may be achieved by injecting a diluent fluid such as a light hydrocarbon fluid or carbon dioxide into the formation.
In some cases, the viscosity of hydrocarbon fluids in a subterranean formation may be decreased both by increasing the temperature of the hydrocarbon fluids in the formation and by diluting the hydrocarbon fluids. For example, in a steam/solvent hybrid process, both steam and a diluent solvent may be injected into the formation to simultaneously heat and dilute the hydrocarbon fluids.
The permeability of a formation may be homogeneous or heterogeneous. In addition, a formation may include one or more discrete permeability barriers. Decreasing the viscosity of the hydrocarbon fluids in the formation may have little effect upon the mobility of the hydrocarbon fluids in the formation if the permeability of the formation is generally low, if the permeability of the formation is heterogeneous, or if there are one or more permeability barriers in the formation.
Furthermore, the presence of low permeability, heterogeneous permeability and/or permeability barriers in a formation may reduce the effectiveness of hydrocarbon recovery processes in the formation.
For example, steam assisted gravity drainage (SAGD) processes and similar processes depend upon permeability of the formation to transfer heat throughout the formation.
Efforts to overcome the effects of low permeability, heterogeneous permeability and/or permeability barriers in a formation are known in the art. Examples include U.S. Pat. No. 4,442,896 (Reale et al), U.S. Pat. No. 4,479,541 (Wang), U.S. Pat. No. 6,708,764 (Zupanick), U.S. Pat. No. 7,069,989 (Marmorshteyn et al), U.S. Pat. No. 7,647,967 (Coleman, II et al), U.S. Patent Application Publication No. US 2010/0078220 A1 (Coleman, II et al), PCT International Publication No. WO 2010/074980 A1 (Carter, Jr.), and PCT International Publication No. WO 2010/087898 (Boone et al).
There remains a need for systems for recovering fluids such as hydrocarbon fluids from a subterranean formation which provide enhanced permeability of the subterranean formation, and for methods for enhancing the permeability of a subterranean formation.